Vacuum tube stem



' Oct. 2, 1934. w w. EITEL ET AL VACUUM TUBE STEM Filed Nov. 5, 1952 INVENTORS WILL/AM W. E/TEL. 8

JACK MCCULLOUGH. MKW

ATTORNEY 2 n w E z zugmiEmmi:J I

LTTT G :1 a w IIPI Patented Oct. 2, 1934 UNITED STATES PATENT OFFICE VACUUM TUBE STEM poration of Nevada Application November 5, 1932, Serial No. 641,399

3 Claims.

Our invention relates to a stem for vacuum tubes, and more particularly to a stem adapted to carry a plurality of leads of relatively large diameter.

Among the objects of our invention are: To provide a stem having a plurality of lead wires, adapted for high power transmitting tubes; to provide a stem permitting maximum separation of a plurality of lead wires in a vacuum tube; to provide a vacuum tube stem in which the seal for leads carrying a large amount of current is kept cool; and to provide a vacuum tube stem having a separate seal for the cathode leads and the leads to the cooperating electrodes.

Other objects of our invention will be apparent or will be specifically pointed out in the description forming a, part of this specification, but we do not limit ourselves to the embodiment of our invention herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawing:

Figure 1 is a longitudinal sectional view of a tube embodying the stem of our invention.

Figure 2 is a cross sectional view taken through the stem as indicated by the line 22 in Figure 1.

Figure 3 is a cross sectional view of the inner end of the stem taken along a plane indicated by the line 3--3 in Figure 1.

In vacuum tubes of high power, particularly those used for radio transmitting purposes in which a multiplicity of grids are used, stem construction is very important particularly as the cathode or cathode heater leads usually carry high currents usually alternating in character, while other leads are sensitive to adjacent fields. It is therefore desirable that all leads be as widely separated as possible, and that provision for cooling the cathode or cathode heater leads be made.

In the drawing, a preferred form of transmitting tube is shown utilizing a stem of our invention which incorporates the desirable qualities above referred to.

An envelope 1 is provided with a double reentrant stem 2 having an outwardly extending pinch 4 through which' heater leads 55 are sealed. The inner circumference 6 of the reentrant stem has four equally spaced electrode leads '7 sealed therethrough, making a total of .six leads through the stem. This construction gives a maximum of separation to the leads and the entire stem is of sturdy construction.

A metal clamp 9 is frictionally applied to the stem, having a small insert of gauze 10 between the clamp and the stem to increase the gripping power of the clamp. Four equally spaced risers 11 are welded to the clamp and support a stemend insulating positioning member 12. This member is preferably a disc of lava, or like ma-- terial, and is drilled with a large number of positioning holes 14.

The electrodes of the tube are all in concentric relation and comprise in order, beginning from the outside, an anode 15 provided with cooling fins 16, an outer grid 17, a central grid 19, an inner grid 20, a cathode cylinder 21, the latter provided with an oxide coating having high electron emitting properties, and a hairpin heater filament 22 positioned inside the cathode cylinder.

The anode and the three grids each have four equally spaced support wires 23 which extend both above and below the body of the electrodes. The cathode cylinder has two stem-end extension wires 24 and two anode end extensions 25. The heater filament is supported at the stem end by heater extensions 26.

All of the support wires and all of the extensions extend through the holes 14 in the positioning member 12, project slightly on the other side, and are held firmly in place by small wire retainers 27 welded one above and one below the positioning member. The stem end, or lower end of the electrodes are thus held in spaced relationship as determined by the spacing and positioning of the holes 14.

While we have shown the support wires and extensions entering the positioning member along the same radii, we find it advantageous to stagger the insertions to obtain greater distances between the leads. In any event the anode leads are inserted preferably midway between the insertion of the risers 11 so that there may be no chance for anode potentials to reach the clamp 9.

The two heater extensions 26 are connected to the heater leads 5 by flexible heater links 29, and one extension from each of the three grids and the cathode cylinder are connected one to each of the electrode leads '7 around the circumference of the stem by flexible electrode links 30.

The entire electrode structure is thus supported by the clamp 9 through the medium of the risers 11 and the stem-end positioning member 12. No shocks or strains of any kind can be transmitted to the leads from the electrode assembly, as the leads are connected to the assembly only through flexible links, and no anode potential is placed on the clamp 9, as the risers 11 are dead-ended at the member 12.

The upper extensions and lead wires project through an anode-end positioning member 31, which in order to reduce weight may be formed as a cross of insulating material of the same kind as the stem-end positioning member. The extensions are secured as in the stern-end member, that is by having a wire retainer 2'7 welded above and below the member.

As the heater filament is in the form of a hairpin, a tension spring 32 is mounted on the top of the member 31, having a hook projecting,

through to engage the apex of the hairpin, and thus maintain it in position.

An anode lead 33 is welded to one of the anode extension wires, of flexible wire and after leaving a small amount of slack, is welded, to an anode lead 34 sealed through the upper end of the envelope. On the exterior this lead is fastened to a cap 35 held to the envelope by cement 36.

A shield 37 either in grid form, or a solid piece of metal, is welded by support wires 38 to the center grid extension, on the top of the upper or anode-end positioning member, and extends over and shields the extensions of the inner grid, the cathode cylinder, and the heater tension spring.

In tubes of large power the leads are all of tungsten sealed into glass or the type known as hard, or hero-silicate glass. The tungsten rods areof large diameter, and if desired, the cathode heater leads 5 may be made larger if desired to Y Y carry heavy currents.

The cathode heater lead seal in the pinch l is removed from influence of the heat generated by the operation of the tube, and a long portion of these leads must be traversed by conducted heat before reaching the seal or pinch. In addition, the pinch is outside the tube in air, and as such tubes are not customarily based in use, is kept cool by air circulation.

The electrode leads '7 are spaced relatively distant from the cathode leads, and it may be desirable to rotate the cathode heater leads 5 to come between the leads 7 rather than in line with them as shown for convenience in the drawing.

Stems such as have been described have been used in tubes of 250 watts power, in envelopes the size of the usual watt tube without stem breakage or other lead-in difiiculties.

We claim:

1. A stem for a vacuum tube consisting of a cylindrical portion sealed to an envelope, to extend within said envelope, a hollow outwardly extending portion having walls continuous with said inwardly extending portion, said outwardly extending portion being within said inwardly extending portion and terminating short of the junction of said cylindrical portion and said envelope, a pinch on said outwardly extending portion, lead wires sealed in said pinch, and a plurality of lead wires sealed through the junction of said inwardly projecting portion with said outwardly projecting portion.

2. A stem for a vacuum tube consisting of a cylindrical portion sealed to an envelope, to extend withinsaid envelope, a hollow outwardly extending portion having walls continuous with said inwardly extending portion, said outwardly extending portion beng within said inwardly extending portion and terminating short of the junction of said cylindrical portion and said envelope, a pinch on said outwardly extending portion, lead wires sealed in said pinch, and a plurality of equally spaced lead wires sealed through the junction of said inwardlyprojecting portion with said outwardly projecting portion.

3. A stem for a vacuum tube having a cathode and cooperating electrodes consisting of a cylindrical portion sealed to an envelope, to extend within said envelope, a hollow outwardly extending portion having walls continuous with said inwardly projecting portion, said outwardly extending portion and terminating short of the junction of said cylindrical portion and said envelope being inside said inwardly projecting portion, a pinch on the end of said outwardly extending portion, cathode lead wires sealed in said pinch, and a plurality of lead wires for said cooperating electrodes being' sealed through the junction of said'inwardly projecting portion'with said outwardly projecting portion.

WILLIAM W. EITEL. JACK MCCULLOUGH. 

